Project Summary Hypertension (HTN) is the most common chronic condition among adults in the United States (US). Uninsured adults are more likely to have undiagnosed HTN, less likely to receive regular screening, and less likely to have their HTN under control than insured adults. Prior studies of individual states' Medicaid expansion showed that gaining insurance increased healthcare service utilization, receipt of recommended preventive care, and improved health outcomes; but these studies were limited by having no comparison group. More recently, multiple states were impacted by federal policy changes (e.g., Affordable Care Act [ACA]), creating `natural experiments' to assess whether and how gaining (or losing) health insurance improves HTN prevention and care. Further, there is variability in how states choose to expand or contract coverage, which creates opportunities to identify `intervention' and `control' states (e.g., some states expanded Medicaid eligibility, while others did not). We are well-poised to study the ACA Medicaid expansion natural policy experiment and other policy changes that may unfold in the next few years. In addition, access to care through health insurance may be insufficient to reduce barriers to HTN care. Thus, other social determinants of health ([SDOH]; e.g., individual- and community-level factors) may differentially affect the relationship between gaining insurance and receiving HTN care. We will use electronic health record (EHR) data from the ADVANCE clinical data research network, linked to community-level SDOH, which has data from 599 community health centers (CHCs), including 376 CHCs in 14 Medicaid expansion states (n=1,139,779 patients) and 224 CHCs in 8 non- expansion states (n=658,306 patients). From this dataset, we will collect detailed information on changes in HTN incidence, screening, treatment, and management comparing states that expanded Medicaid, and those that did not. The specific aims are as follows: Aim 1. Compare HTN incidence, prevalence of undiagnosed HTN, and rates of HTN screening, in Medicaid expansion versus non-expansion states before and after the ACA. Aim 2. Compare HTN treatment and management in Medicaid expansion versus non-expansion states, before and after the ACA. Aim 3. Assess the extent to which rates of HTN incidence, screening, and treatment effectiveness among patients who gained insurance versus those continuously insured or uninsured, pre-post ACA, are moderated by individual-level SDOH (e.g., race, ethnicity). Aim 4. Explore the interaction between community-level SDOH (e.g., neighborhood racial segregation and deprivation) and HTN screening, treatment, and management among patients who gained insurance relative to those who were already insured or uninsured, in expansion states. We will build directly on our preliminary work and take advantage of the diverse strengths of our multidisciplinary team. The ADVANCE dataset uniquely positions us to assess current and future natural experiments. Findings will be relevant to policy and practice changes aimed at mitigating disparities in HTN care for vulnerable populations.